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<TITLE>An Introduction to Scheme and its Implementation - Returns and Parentheses</TITLE>
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<H3><A NAME="SEC89" HREF="schintro_toc.html#SEC89">Returns and Parentheses</A></H3>

<P>
A common mistake in Scheme is to forget the closing parentheses of
expressions.  If you forget a closing parentheses--usually because
you need several to close nested expressions--most systems will just
hang, waiting you to finish typing the expression.

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This is a feature, not a bug.  It lets you put <CODE>&#60;RETURN&#62;</CODE>s (line
breaks) in your input, to format the code on the screen as you type it in.
When you type in the last closing expression and hit <CODE>&#60;RETURN&#62;</CODE> again,
Scheme recognizes that you've typed in a whole expression, and evaluates
it and prints the result.

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<P>
So if you type in an expression and hit <CODE>&#60;RETURN&#62;</CODE>, and Scheme doesn't
do anything, check to see if you closed all of the parentheses you opened.
If not, just type in the missing parenthesis and hit <CODE>&#60;RETURN&#62;</CODE> again.

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<P>
(It's also possible that in your system, you have to do something
special to get Scheme to evaluate an expression--like hitting a
different key, or clicking on a button or a menu item.  In such
systems, <CODE>&#60;return&#62;</CODE> may be only for formatting the text you're
inputting, and another key tells Scheme to go ahead and evaluate
what you've typed.)

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